1. Field of the Invention
The present invention relates to a filter device and a liquid drop ejecting device, and in more detail, to a filter device that removes refuse and foreign matter from liquid, and to a liquid drop ejecting device that ejects, from nozzles of a liquid drop ejecting head, liquid which has passed through the filter device and been supplied.
2. Description of the Related Art
In an inkjet recording device carrying out printing onto a recording medium by ejecting ink drops from nozzles of a recording head, in order to prevent deterioration in the ink ejecting performance or clogging of the nozzles due to refuse and foreign matter existing in the ink, a filter which removes the refuse and foreign matter in the ink is provided on the path by which ink is supplied to the recording head.
On the other hand, in inkjet recording heads in recent years, for the purpose of high-speed printing, there has been the trend to increase the number of nozzles provided at a single recording head, or to make the repetition frequency of ink jetting larger. Further, for the purpose of high image quality printing, the trend toward making the diameter of the nozzle smaller in order to make the jetted ink drop smaller has progressed.
For these reasons, the ability to remove even finer refuse and foreign matter, and a configuration having a small pressure loss, have been required of the aforementioned filter. To this end, trends toward making the mesh of the filter finer and making the surface area of the filter larger have advanced. However, if the surface area of the filter is made to be large, the inkjet recording head becomes large due to the placement of the filter. As a measure for addressing this, it has been thought to suppress the increase in the size of the inkjet recording head by dividing the filter into plural sections and placing the plural sections in parallel.
However, in the above-described structure, the flow path at the downstream side of the filter branches off in plural directions. Therefore, in a case in which an air bubble which has arisen in the ink stops in one of the flow paths, the flow speed in the other flow path increases. The ability to remove (ability to discharge) the air bubble in the flow path in which the air bubble has stopped worsens, which leads to a deterioration in the ink ejecting performance.
FIG. 14 is a drawing which shows, schematically and in a simplified manner, a filter unit (filter device).
As shown in FIG. 14, a filter unit 910 is provided at an ink flow path between an ink tank (not shown) and an inkjet recording head 902. The inkjet recording head 902 ejects ink drops from nozzles (not shown) formed in a nozzle surface 904 onto a recording sheet which is a recording medium, so as to form an image on the recording sheet.
The filter unit 910 has a first ink chamber 912 and a second ink chamber 914. The first ink chamber 912 and the second ink chamber 914 are partitioned by a filter 916.
An ink supply path 924 and an ink circulating path 926 communicate with the first ink chamber 912. An ink feed-out path 930 communicates with the second ink chamber 914. The ink in the ink tank (not shown) is supplied from the ink supply path 924, and is fed to the inkjet recording head 902 from the ink feed-out path 930. Further, the ink in the first ink chamber 912 can circulate to the ink tank from the ink circulating path 926.
Note that the first ink chamber 912 corresponds to an outer chamber, whereas the second ink chamber 914 corresponds to an inner chamber.
First, the discharging of air at the time when ink is initially filled into the filter unit 910 will be described.
As shown in FIGS. 15(a) and (b), ink is poured into the first ink chamber 912 from the ink supply path 924, and the ink is gradually filled into the first ink chamber 912 and the second ink chamber 914.
At this time, when the lower end portion of the filter 916 which partitions the first ink chamber 912 and the second ink chamber 914 is submerged in the ink, the ink seeps toward the upper portion of the filter 916 due to capillary action. The entire surface of the filter 916 is wet by the ink before the first ink chamber 912 and the second ink chamber 914 are filled with ink.
When the entire surface of the filter 916 is wet by ink, the entry and exit of air between the first ink chamber 912 and the second ink chamber 914 via the filter 916 is impeded. Therefore, air within the second ink chamber 914 cannot be discharged-out through the ink circulating path 926. Accordingly, the air within the second ink chamber 914 can only be discharged-out through the inkjet recording head 902 which has a high discharge resistance.
Thus, as shown in FIG. 15(c), the liquid surfaces of the first ink chamber 912 and the second ink chamber 914, which had been maintained the same until then, are no longer the same. The first ink chamber 912, from which air is discharged from the ink circulating path 926 which has low resistance, is filled with ink first.
As shown in FIG. 15(d), when the first ink chamber 912 is filled with ink, the pouring of ink into the second ink chamber 914 begins again.
Then, as shown in FIG. 15(e), when the liquid surface reaches the height of a feed-out path entrance 930A of the ink feed-out path 930, ink is discharged from the ink feed-out path 930, and the supply of ink to the inkjet recording head 902 begins.
At this time, because the cross-sectional surface area of the ink feed-out path 930 is large, the ink goes along the wall surface of the ink flow path 930 (like a waterfall), and flows into the inkjet recording head 902. In other words, the ink flows into the inkjet recording head 902 in a state in which no meniscus is formed.
Therefore, as shown in FIG. 15(f), the ink is fed to the inkjet recording head 902 in a state in which ink and air are mixed together.
A large amount of air K remains at the ceiling portion of the second ink chamber 914. Due to the filter 916, it is difficult for this air K to move to the first ink chamber 912, and therefore, the air K continues to remain in the filter unit 910.
As shown in FIG. 16, because the feed-out path entrance 930A of the ink feed-out path 930 opens in a vicinity of the ceiling portion, the air K which is remaining is in a vicinity of the feed-out path entrance 930A.
Thus, at the time of an ink suction operation which sucks the ink from the nozzles of the inkjet recording head 902, or the like, due to the ink which is flowing as shown by arrow Y9, the air which is remaining becomes fine air bubbles which enter into the ink feed-out path 930 from the feed-out path entrance 930A and flow into the inkjet recording head 902.
When air flows into the inkjet recording head 902 together with the ink in this way, the reliability of the inkjet recording head 902 markedly deteriorates.
Accordingly, it is desirable to make it difficult for air remaining in a filter unit to flow-out.